The present invention relates to the field of wireless communications. More specifically, the present invention relates to the field of third generation 3G wireless communications employing Time Division Duplex (TDD) and to frequency error detection and correction within a wireless communication system receiver.
In typical wireless communications systems, a frequency difference between the transmitter and receiver local oscillators can prevent the transmission of data. Additionally, because many systems utilize the same Local Oscillator (LO) for both receiver and transmitter functions, a large frequency offset can cause significant out-of-band interference.
In order to overcome this problem, prior systems have utilized differential detection of phase or applied the Discrete Fourier Transform to estimate the frequency error and apply an update to the Local Oscillator. However, these prior systems either ignored the effects of multipath interference or combined the AFC with a RAKE receiver. Therefore, these prior techniques were not applicable for systems that use Multi-user Detection without a RAKE receiver.
The present invention enables detection and correction of the oscillator frequency error within a wireless communication system receiver. Moreover, the present invention provides robust performance in the presence of multipath interference. Furthermore, the present invention overcomes the interference problem as well as exploiting the diversity gains associated with large delay spread. Additionally the inventor provides the capability of rejecting inter-cell and intra-cell interference sources, while operating effectively in the presence of both RF carrier offset and sampling clock offset. Also, the present invention has adaptive tuning speed and functions with systems using Multi-user Detection algorithms without RAKE receivers and can operate on a discontinuous pilot (training) signal.
The present invention includes a frequency estimator having block correlators, conjugate product and sum block, accumulation block, multipath detection and a loop filter (adaptive bandwith). The multipath detection includes a search block, threshold detection block and a block for combining multipath components.